Constrained Morph dragging

> Hello Morphic experts,
>
> I am learning / experimenting with Morphic and have the following question:
>
> "How do I constrain the movement of a dragged Morph?"
>
> As illustrated here:
>
> http://jqueryui.com/draggable/#constrain-movement
>
> (e.g. constrain within axis/container)
>
> So far the "hack" I came up with was to aggresively re-position the
> dragged Morph in its "drawOn:", if it is attached to a HandMorph:
>
> drawOn: aCanvas
>         self owner isHandMorph "is there a better way to ask: am I being dragged?"
>                 ifTrue: [ self position: (self position x) @ 400 ].
>         super drawOn: aCanvas.
>
>
> I am sure this solution is pretty bad... I also get visual artifacts
> when I move the mouse up/down.
>
> Are there better ways/hooks for this?
>
> Generally: is there a method that is called on submorphs whenever the
> parent Morph was re-positioned/re-sized?
>

> I came up with this... does what I need and I have  no visual
> artifacts anymore. Still, I'm not happy for having to override a
> private method in order for this to work... :-/
>
> Overridden existing method in my Morph subclass:
>
> privateFullMoveBy: delta
>         super privateFullMoveBy: delta.
>         (self wantsToConstrainDragging & self isBeingDragged)
>                 ifTrue: [ self adjustPositionWhileDragging ]
>
> New methods in my Morph subclass:
>
> isBeingDragged
>         ^ self owner isHandMorph
>
> wantsToConstrainDragging
>         ^ true
>
> adjustPositionWhileDragging
>         self position: (self constrainedDragPositionFrom: (self topLeft))
>
> constrainedDragPositionFrom: aNonConstrainedPosition
>         "Adjust the position to be constrained however you want. In this case
> horizontally at y=450"
>         ^ (aNonConstrainedPosition x) @ 450.
>
> You would need to override only "wantsToConstrainDragging" and
> "constrainedDragPositionFor:".
>
> Any critique to the code and/or naming welcome! :-)